The answer is D) Organisms in the population must express no mating preferences.
Some of the conditions that must be met for a population or an allele to be in Hardy-Weinberg equilibrium are:
1. The population must be very large - so A) could not be the right answer.
2. There must be no migration and population must be isolated - so B) could not be the right answer.
3. There must be no mutations - so C) could not be the right answer.
4. There must be random mating, which means there are no mating preferences - so, D) is the right answer.